6061 billet aluminum plugs to install on all previously machined heads where the automatic will no longer be used. Rather than keep the steel release in there and create a hot spot, replace with these aluminum plugs. Great option for when you’re machining a 15 / 20 / 30° squish band and you get into the bolt. 1 length available, if you have the shorter version (used very little) you will need to shorten them.